Fire alarm system



Jan. 21, 1936. O, I, H E MAN 2,028,653

' FIRE ALARM SYSTEM Filed May 19, 1951 2 Shets-Sheet 1 Jan. 21; 193%. 0.l. H. EKMAN 2,028,653

'FIRE ALARM SYSTEM Filed May 19, 1951 2 Sheets-Sheet 2 lv m/q PatentedJan. 21, 1936 UNITED STATES PATENT OFFICE FIRE ALARM SYSTEM ApplicationMay 19, 1931, Serial No. 538,568 In Sweden May 7, 1930 4 Claims.

In modern automatic fire alarm systems closed circuit current is used inorder that the plant shall be under permanent control, said currentpassing through electric circuits containing heat sensitive switches orthermostats disposed at different places in the localities to beprotected against fire and adapted, when heated, to interrupt saidclosed circuit current thereby causing an alarm device to be released.In order that a simple conductor breakage shall not wrongly produce afire alarm signal it is now customary to arrange the system in such away that the circuits or loops extending through the localities to beprotected and including the thermostats are made with double or multipleconductors and provided with such relay means that an alarm signal isproduced only when a line interruption occurs simultaneously in allconductors in such a double or multiple loop. Hitherto the differentloops have been parallel-connected with each other which arrangementleads to an unnecessarily high closed circuit current consumption withconsequent extra costs for loading a storage battery etc.

The present invention has for its object to bring about a simple andinexpensive but nevertheless reliable automatic fire alarm system withtwo or more conductors in the loops containing the thermostats and issubstantially characterized by that the conductors in each individualloop are permanently connected in parallel whereas the difierent loopsare connected in series with each other and connected to a relay meanswhich is common to all the loops and adapted to selectively indicate aninterruption in a loop conductor or a short circuit between the loopconductors and to produce an alarm signal only upon an interruption inall of said conductors occurring, the loops being also provided with asection indicating device adapted to mark the loop in which aninterruption in a single conductor or an interruption in all conductorshas occurred.

The invention will be more closely described with reference to theaccompanying drawings. Figure 1 is a circuit diagram for an automaticfire alarm plant according to the invention with section relays (doublewound) common to the twoloop conductors in a loop for marking thesection or loop in which an interruption or a short circuit hasoccurred. Figure 2 shows another embodiment with separate section relayswhich at the same time serve as auxiliary relays for producing a firealarm signal. Figure 3 shows a modification of the arrangement accordingto Figure 1 with normally disconnected section relays which areconnected into circuit with time lag and also serve as auxiliary relaysfor producing fire alarm signals.

In Figure l, I and II designate two series-connected loops or sectionseach consisting of two permanently parallel-connected conductors a, b,said loops or sections including a plurality 01' double thermostats Tadapted to fuse in the event of a fire and to then simultaneously bringabout an interruption in the loop conductors w, I). Said loops are inknown manner extending through the localities to be protected againstfire whereas the portion of the plant indicated under the horizontal dotand dash line is disposed on a central switch board in the building.Only two loops are shown but several loops may be connected in series inan analogous manner. B is the central battery which on account of thesmall current consumption in a plant according to the invention mayconsist of a dry battery, whereas in hitherto known plants it has beennecessary to use storage batteries with expensive charging devices onaccount of the high closed circuit current consumption. Between thepoles of the battery B the parallel conductors a and b are included in amain circuit which in each of the parallel branches formed by saidconductors includes a control relay and a resistance. Thus a lowresistance Ma and a control relay Ra having a high resistance areincluded in the a-conductor whereas a high resistance Mb and a controlrelay Rb are included in the b-conductor. The control relays Ra and. Rhare normally passed by closed circuit current, then holding theircontacts broken, whereas upon an interruption occurring in thecorresponding loop conductor the appertaining control relay isde-energized, then closing its contacts. Shunted between the ends of theaand b-branches in the respective loops or sections are the sectionrelays SR1, SRu, each of said relays being provided with two windings ona common iron core and a common contact. In said relays the coilsdesignated a: and 0.11 are shunted between the ends of the a-conductorsin the loops I and II respectively whereas the coils in and bu areshunted to the corresponding bconductor. When passed by current each ofthe windings an, an, in, bn produces a magnet field suificiently strongto alone attract the corresponding armature, and the two windings on acertain relay, by way of example in, b; of the re lay SR1, are wound insuch a way that they cooperate when simultaneously passed by current.BRR is an alarm-box control relay which is normally energized by theclosed circuit current and serves to indicate that the circuit for theelectric release of the alarm-box magnet BM is not broken and that theclock-work in the alarmbox is wound. up, a mechanically controlledcontact kg in the alarm-box being opened when said clock-work is rundown. FR is a fault relay common to the Whole system which relay whenenergized in known manner connects a bell or an optical fault signallingdevice (not shown) into circuit.

The described arrangement operates in the following manner. Upon aninterruption occurring in only one loop conductor, say the a-conductorof the loop I, the corresponding control relay Ra is de-energized at thenormally closed circuit from the minus pole of the battery through therelay Ra the loops a of section I and II resistance Ma plus pole of thebattery is broken, and releases its armature whereby its contact K4 isclosed. This has, however, no effect on the alarm-box magnet BM as thecircuit for said magnet is broken at the contact 702 of the othercontrol relay Rb connected in series with the contact k1. As theshort-circuit of the winding er of the section relay SR: normally causedby the a-conductor in the loop I is removed on account of theinterruption said section relay is energized over a circuit traced asfollows: From minus pole of the battery over contact K4 of the relay Rathe upper winding of the relay SR1 the loop a of the section IIresistance Ma, plus pole of the battery. The relay SR1 therefore closesits contact k6 whereby the section lamp SL1 is lit and the fault relayFR energized, thereby marking the fault.

Each of the control relays R9. and Rh is provided with a contact k4which short-circuits the relay winding when the relay drops its armaturewhereby the current through the windings of the section relays SR: andSR1: becomes stronger than otherwise would be the case.

Upon a simultaneous interruption in both the aand b-conductors, whichoccurs practically only at the event of a fire, both control relays Ra,which is normally energized over the abovementioned circuit, and Rb,which is normally energized over a circuit from the minus pole of thebattery through resistance Mb over conductor b in sections I and II,winding of relay Rb to plus pole of the battery, drop their armatures,the contacts 761 and k2 being then simultaneously closed and the batteryB connected directly to the alarm-box magnet releasing the same so thatan alarm signal is produced. The said circuit is traced as follows: Fromthe minus pole of the battery over contact K1 of the relay Ra, overcontact K2 of the relay Rb, over contact K3 of the alarm box magnet,through the winding of said magnet to the plus pole of the battery.Normally the battery is connected to the alarm-box magnet BM over thealarm-box control relay BRR having a high resistance, but the weakclosed circuit current then occurring is not suificiently strong torelease the magnet BM. When the contacts In and k2 are closed said relayBRR is shunted whereby full current strength is obtained through thealarm-box magnet BM, which is then released as mentioned above. If, forexample, the interruptions are located in the section I both windings(11, hr of the section relay SR will become energized and co-operate toattract the armature of the relay whereby the section lamp SL1 is litindicating that the release of the alarm magnet has been caused by aninterruption insaid section. r

If a short-circuit should occur between the aand b-conductors of a loopthe control relay Ra will still remain energized for the reason that itis connected in parallel with the high resistance Mb so that asufficiently high voltage drop exists between the ends of the winding ofsaid relay. The control relay Rb, which is parallel-connected with thelow-ohmic current limiting resistance Ma, will, on the other hand, bede-energized, its contact k5 being then closed causing a current to passthrough the fault relay FR over a circuit from the minus pole of thebattery through the winding of the relay FR, the low ohmicresistance r,the contact K5 of the relay Rb to the plus pole of the battery. Therelay FR attracts its armature and marks the fault. The section relaysSR1 and SR1: still remain short-circuited by the loop conductors andconsequently do not operate. If, when the fault relay FR attracts itsarmature, the section lamp SL1 or SLn is not lit this is an indicationthat the marked fault is a short-circuit and not a conductorinterruption. The section relays SR1 and SR1: which, as alreadymentioned, upon an interruption occurring are series connected with thecontrol relays Ra and Rh should have high resistances as compared withthe resistances of the latter relays in order considerably to reduce thevoltages on the same so that the relays RB. and Rb positively drop theirarmatures and remain with their armatures released.

The arrangement shown in Figure 2 differs from the one shown in Figure 1partially therein that the section relays are divided on two relaysSRra, SRIb and sRIIa, sRIIb respectively corresponding to the foursimple windings 11.1, In, an, bn in Figure 1. Further, double faultrelays FRa and FRb each having a group of signal lamps SL9. and SL1) areprovided, one group for the a-conductors and one for the b-conductors.In addition to the ordinary contacts k6 for lighting the signal lampsand magnetizing the fault relays the section relays are also providedwith extra contacts k7 and k8 which are series-connected within eachcouple of relays SRm, SRrb and SRIIa, sR-IIb respectively appertainingto a section.

The arrangements according to Figure 1 is further attended by theinconvenience that the section relays are always connected into circuit.At a possible short-circuit within the coils of said relays the closedcircuit current for the control relays Ra, Rb will remain closed overthe shortcircuited windings of the section relays even if a doubleinterruption in the loops exists wherefore such a short circuit makesthe fire alarm system inoperative. Said inconvenience is eliminated whenusing the system shown in Figure 2 in which the section relays sRIa,sRIb, SR-m. and SRIIb are normally disconnected and connected intocircuit first after the corresponding control relays R3. or Rb have beende-energized and the corresponding fault relay FRa or FRb has operated.

In the two parallel main circuits leading from the two poles of thebattery B through the aand b-conductors in Figure 2 only the two controlrelays Ba and Rb and the resistances Ma and Mb are included. Besidesbeing provided with the ordinary contacts 704 for short-circuiting therelay-windings when the relays are ole-energized and with theseries-connected contacts 701 and kn for producing a fire alarm signal(by means of the alarm-box magnet BM) the relays Re and Rb are eachprovided with an extra contact 769 adapted to close the current throughthe appertaining fault relay m or FRb respectively when the controlrelay drops its armature (upon a. single or a double line interruptionor a short circuit occurring).

Each of said fault relays FRa and FRb is provided with a contact km forclosing the circuit of a fault indicating device indicated on thedrawing as a bell KL, and also with an extra contact 761a, km. or krb,knb respectively for each section. Each of the last mentioned contactsis included in the circuit of the corresponding section relay SRIa,sRIIa etc. having the same index. All section relays are thus normallydisconnected and are connected into circuit first after a correspondingcontrol relay Ra o'r Rb has been deenergized and has connected theappertaining fault relay FRE or FRb into circuit, at the con tacts 701a,krb etc. of which relay the circuits for the section relays are thenclosed. The section relays are as already mentioned provided withcontacts ks for lighting the signalling lamps SL@ and SLb and also withseries-connected contacts 757 and k8 for auxiliary release of thealarm-box magnet BM in case the contacts 101 and k2 should fail, forinstance not be clean or stick.

The plant according to Figure 2 operates safely also in case ashort-circuit in the windings of the section relays should occur. Insaid embodiment the loops are normally included in lines which onlycontain the control relays Ba and Rb, the battery B and the resistancesMa and Mb but no other relay windings or resistances, which ensures thata closed circuit current strength the control relays Ra, Rb willactually be broken upon an interruption in a loop conductor occurringand not maintained over any path of leakage. The control relays Ra andRb thereupon connect the fault relays PBS. and FRb into circuit whilesimultaneously releasing the alarm-box magnet BM in case a doubleinterruption has occurred, the fault relay FRb and FRb finallyconnecting the section relays SRIb, SRIb etc. into circuit. Said relaysbeing thus energized with time lag in relation to the control relays Raand Rb first after the latter have performed their alarm function.Possible short circuits in the section relays therefore cannot preventthe release of the alarm-box magnet BM. The extra impulse thereaftersent out from the section relays SRIa, SRib etc. to the alarm-box magnetBM increase the likelihood that said magnet will actually be released.

The plant according to the invention may also in known manner beprovided with relays for indicating earthing of the loop conductors.

Certain modifications may be made in the described arrangements withoutdeparting from the spirit of the invention. The resistance Ma may, forinstance, be entirely dispensed with or substituted by a relay having alow resistance which relay is energized upon a short-circuit and isprovided with a separate short-circuit indicating device, by way ofexample an optical device. The relay Rb is then made with a higherresistance so that it does not drop its armature upon a short circuitoccurring.

Further, the simple control relays Rb and Rb may each be substituted bytwo or more seriesconnected relays in order to increase the safety ofoperation, as in this case at least any of the series-connected relaysmust drop its armature upon an interruption occurring in the loopconductors. The short-circuiting contact K4 of the control relay Rbshown in Figures 1 and 2 may also be adapted to short-circuit theresistance Mb as well as the own winding of the relay when the relaydrops its armature in order to reduce the resistance in the circuits forthe section relays and, if desired, for the fault relays in case saidrelays are connected in series with the section relays (compare Figurel).

The series-connected normally open contacts 701 and kg of the controlrelays Ra and Rb may be substituted by parallel-connected normallyclosed contacts for opening the circuit of a special alarm relaycontrolled by closed circuit current which relay in turn, upon asimultaneous opening of said two parallel contacts, closes the circuitthrough the alarm-box magnet BM in order to release the same. Also theremaining normally open contacts may in similar manner be exchangedagainst normally closed contacts for closed circuit currents withoutconsiderably altering the rest of the plant.

In very large systems having several sections the embodiment shown inFigure 2 has the inconvenience that it is difiicult to obtain faultrelays FRa and FRb having a sufiiciently large number of contacts 701b,kIIa etc. This difiiculty may be eliminated by connecting several faultrelays in parallel or by providing each section relay sRIa, SRIb etc.with an extra contact closing the interruption km, 7cm etc. in the nextfollowing section. The fault relay, by way of example FRa, then only hasto close the circuit for the first section relay SRIa which then closesthe circuit for the other section relay sRIIa etc.

It will be understood that in automatic fire alarm systems ordinaryswitches, isolating switches, etc. for the supervision of the system maybe provided.

I claim:-

1. In an automatic fire alarm system, a protective circuit including aplurality of loops each made up of two adjacent parallelly extendingconductora the corresponding conductors of all loops being connected inseries so as to form two circuit branches connected in parallel to acommon source of current, thermostatic circuit breakers inserted in bothconductors of each loop, a first electromagnet coil in one of saidcircuit branches, a second electromagnet coil in the other of saidbranches, an alarm, contact means and connections controlled by saidelectro-magnet coils, jointly, for closing a circuit through the alarmon the de-energization of both conductors, indicating means individualto each loop including two windings, each normally shortcircuited by oneloop conductor, an indicator for each loop and connections and contactmeans controlled by said windings to close a circuit through acorresponding indicator, on a break in any loop.

2. An automatic fire alarm system as claimed in claim 1, in which thetwo electromagnet coils are arranged in common to all loops.

3. In an automatic fire alarm system, a protective circuit including aplurality of loops each made up of two adjacent parallelly extendingconductors, the corresponding conductors of all loops being connected inseries so as to form two circuit branches connected in parallel to acommon source of current, thermostatic circuit breakers inserted in bothconductors of each loop, two relays allotted to each loop, a winding oneach relay normally short-circuited by thecorresponding loop conductor,an alarm contact means and connections controlled by said relays jointlyfor closing a circuit through the alarm on a break in the loop, anindicator for each loop, and

connections and contact means controlled by said relays to close acircuit through a corresponding indicator on a break in any loop.

4. In an automatic fire alarm system, a protective circuit including aplurality of loops each made up of two adjacent parallelly extendingconductors, the corresponding conductors of all loops being connected inseries so as to form two circuit branches connected in parallel to acommon source of current, thermostatic circuit breakers inserted in bothconductors of each loop, a first electromagnet coil inserted in onecircuit branch at the positive pole of the current source, a resistanceinserted in the same circuit branch, at the negative pole of the currentsource, a

second electromagnet coil inserted in the other circuit branch at thenegative pole of the current source, another resistance inserted in thecircuit branch last mentioned at the positive pole of the currentsource, an alarm, contact means and connections controlled by saidelectromagnet coils jointly for closing a circuit through the alarm onthe de-energization of both conductors, in-

' dicating means individual to each loop including

